Many manufacturing processes require complex industrial machines utilizing rotating or reciprocating elements. The efficient operation and maintenance of these machines as essential to maximizing production and minimizing downtime. When a rotating machine element acquires a defect, that defect is seldom catastrophic at onset. Instead, the defect is usually of a latent or incipient nature, such as a hairline fracture in the tooth of a gear. Notwithstanding a probable reduction in the efficiency of the machine, if such a fault is not detected, isolated, and repaired, it could grow into a catastrophic failure of the machine with resultant loss of production capacity of the machine and possible injury to personnel. Unfortunately, due to the noise generated by these machines and the acoustic environment in which they normally operate, it is often difficult if not impossible to detect latent or even incipient defects in rotating elements of the machine by visual or aural inspection. Further complicating the detection of such faults is that faulty components may be hidden from view, such as a single gear in an enclosed gearbox.
It is desirable to detect and locate faults while the machine is operating in its normal environment so as not to interfere with the production process. Taking the machine off line to perform preventative maintenance creates an undesirable and inefficient situation, requiring a back-up or redundant machine in order to prevent a shutdown of the production process.
Nonintrusive fault detection may be accomplished by monitoring certain physical characteristics of the machine, such as vibration and temperature levels, using electrical sensors such as accelerometers and temperature sensors. These sensors are typically connected by means of at least one pair of wires per sensor to a monitoring device. The monitoring device processes the sensor signals and produces an output signal which is indicative of the operational health of the machine. Such fault detection devices provide an early indication of machine problems, typically before a catastrophic failure occurs.
One problem associated with wired fault detection systems is the high cost of installation in a typical manufacturing plant. A typical machine may require four to eight vibration sensors mounted at various locations on the machine, and there may be from several dozen to several hundred machines in a typical plant. It is desirable to monitor all of the machines from a central location in the plant, so that manufacturing personnel need not travel to each machine in the plant to assess its health. The installation of wire and conduits to connect each sensor to a central monitoring station could be cost prohibitive.
In addition to installation problems, wired systems are difficult and costly to maintain. Such systems tend to be fragile, primarily due to the wiring. Wires and connectors can easily become contaminated with water or other materials common in dirty industrial environments, resulting in anomalous signals and other failure conditions. Wires are also easily damaged, especially near the connectors, during normal machine maintenance procedures. Such damage is usually manifested as intermittent anomalous signals, which make isolation, diagnosis, and correction of the problem quite difficult.
Wired machine monitoring systems are also inflexible once installed. It is difficult to change the configuration of the system as needs change within the manufacturing plant. If a plant operator decides that more sensors should be added to a machine, or that the location of the machine or sensors should be changed, the cost and difficulties associated with installing additional wiring and conduits must be endured.
Since the major problems associated with wired machine monitoring systems are caused by the presence of the wires, a need exists for a wireless machine monitoring system.